We are studying the follicular cells in insects as a model system of programmed, differentiation-specific protein synthesis in eucaryotes. These cells produce and secrete a family of structural proteins, the chorion proteins, during a defined period of differentiation. During this time, virtually only chorion proteins are synthesized by these cells. The synthesis of each protein proceeds according to strict developmental kinetics, characteristic for each. Thus, differentiation in this system is expressed as a regulated series of protein synthetic changes. We are attempting to understand the basis of this regulation. We are proposing to study the structure-function and evolution of the chorion proteins, which may be coded for by an "information multigene family"; to document the developmental kinetics of specific protein synthesis and corresponding mRNA synthesis, at a high resolution; to characterize the chorion genes by hybridization methods, study their linkage relationships, and begin their purification; to analyze the biochemical effects of what may be regulatory chorion mutants in Bombyx; and to develop the chorion system in Drosophila as a system in which differentiation can be studied by a combination of biochemical and thorough genetic analysis.